The publication DE102011004772A1 for example is known from the prior art. Said publication discloses a method for adjusting the clamping force that is exerted by a parking brake and is generated at least in part by an electromechanical braking device having an electric brake motor. During the procedure, the magnitude of the mechanical work that is produced by means of the actuator is ascertained and the application process is performed until the magnitude of the mechanical work that has been produced achieves a threshold value. In order to ascertain the magnitude of the electrical work that has been produced, electrical variables are used, said electrical variables being in particular the current and the voltage of the electric brake motor that are ascertained preferably directly or indirectly by means of sensors and are present as measured values.
The publication DE102004021534A1 is likewise known. This document relates to a method for an automated parking brake application process that in the case of a motor vehicle leads to an automated parking brake being locked. The core of this prior art resides in the fact that the automated parking brake application process can be performed in a normal operation and in a test operation, wherein the normal operation and the test operation differ at least in terms of the speed at which the parking brake application process is performed. In the test operation, the braking force is initially built up by means of a hydraulic wheel pressure and subsequently the braking force that has been built up in a hydraulic manner is transferred to a mechanical braking force holding device. This prior art discloses that parallel to transferring the hydraulic pressure or after transferring the hydraulic pressure the pressure drops back and when the parking brake is in the locked state the braking force is produced by means of the mechanical braking force holding device independently of the presence of the hydraulic pressure, wherein the magnitude of the braking force that has been built up in a hydraulic manner depends upon the length of time the operating element has been actuated without interruption.
In order to ascertain and adjust a clamping force of a parking brake, the clamping force is estimated by way of example by means of the work that has been produced. Above a defined threshold, the control procedure is switched off accordingly. The minimal clamping force that can be reliably detected in this case is however relatively high since the error component in the case of higher currents is lower. Therefore, malfunctions in the case of higher currents have little effect but malfunctions in the case of lower currents have a greater effect. Furthermore, a multiplicity of operating situations requires a small first force level. Likewise, specific operating conditions do not allow a rapid build-up of a clamping force of the parking brake. The clamping force is therefore built up in the prior art by way of example by means of the hydraulic brake.
In order to be able to continue to use the parking brake for operating situations of this type, it is necessary to design the procedure of controlling the parking brake actuator in such a manner that said parking brake actuator can be adjusted to meet the requirements of the respective operating situation. Furthermore, a sensitive procedure of controlling the parking brake is advantageous. In particular, information relating to an increase in the clamping force is required. This information must be robust, in other words essentially error-free. There is also the requirement for this information to be ascertained as quickly as possible and consequently for said information to be available.